I didn't know they still sold the old stuff. Buying the rainproof in 30 takes the gambling out of it.I think it's more like 12 hours for this stuff? But it also claims to last 6 months and that's wrong by double. I try to do what I can to plan for it not to rain long enough for the stuff to visibly start dying and usually thats 2-3 days.
On the plus side, I usually can't spray at all for several more weeks because it will normally rain almost every day this time of year. So...